Eyelash detection is an important step during the period of iris recognition preprocessing. An eyelash extraction algorithm based on improved ant colony algorithm is proposed. Firstly, by introducing direction factor of inside the eyelash region and outside the eyelash region, the artificial ant can gather to the eyelash-edge quickly, increasing pheromone intensity of eyelash-edge and decreasing that of non-eyelash-edge. At the same time, global and local strategies are taken respectively to update pheromone. After that, the OTSU algorithm is used to segment eyelash edge according to the pheromone intensity of image. Finally, by integrating the eyelash-edge and deleting the noise, the eyelash can be obtained. Experimental results show that, compared with other concerned algorithms, the effect of the proposed method is better than that of others, and when the distance between artificial ants is about 25 pixels, the algorithm can not only ensure eyelash detection speed but guarantee the detection effect.